Lithostratigraphic and geochronologic data from Yukon Territory indicate relatively limited glaciation in the northern Canadian Cordillera during the early Wisconsinan. If the Cordilleran Ice Sheet existed in south and central Yukon during the early Wisconsinan, it was less extensive than during either the Illinoian or late Wisconsinan. In contrast, ice cover during the early Wisconsinan in British Columbia and northern Washington may have been comparable to that of the late Wisconsinan, as suggested by the widespread occurrence of glacial deposits between middle Wisconsinan and presumed Sangamonian nonglacial strata. Sediments of probable Sangamonian age have been studied for pollen and plant and animal macrofossils. Climate during deposition of these sediments was warmer and drier than today. Plant communities probably had different distributions than at present, and permafrost may have been absent or more restricted over some areas in which it currently occurs. Little is known about the transition from the Sangamonian to the early Wisconsinan in western Canada and Washington, although limited data suggest that during the early and middle Wisconsinan there were perturbations in climate ranging from full glacial to temperate.